System and method for intraluminal imaging

ABSTRACT

An improved catheter system having an ultrasonic imaging transducer coupled to a drive cable disposed within a lumen of a flexible tubular catheter body. An improvement including a reconfiguration of the ferrites in the hub assembly, such that the need for the gap between the ferrites is removed. A strain relief member is provide to increase the strength of the electrical transmission lines to enable them to withstand the tensile forces caused by either flushing and/or pull-back operations. A device which allows the electrical transmission lines to extend their length when placed in tension may also be employed to provide strain relief to the electrical transmission lines. Another improvement includes a counter-wound coil structure, which may either expand or contract as the drive cable is being rotated to strengthen the drive cable. The distal tip of the catheter body may be redesigned to provide a lumen which allows for the release of flushing fluids through a distal port in the guidewire lumen.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority fromProvisional Application Serial No. 60/105,475, filed Oct. 23, 1998,incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to medical devices andmore particularly to an improved catheter system having a work elementcoupled to a drive cable disposed within a lumen of a flexible tubularcatheter body.

[0004] 2. Description of the Background Art

[0005] Arteriosclerosis, also known as atherosclerosis, is a commonhuman ailment arising from the deposition of fatty-like substances,referred to as atheromas or plaque, on the walls of blood vessels. Suchdeposits occur in both the peripheral blood vessels, which feed thelimbs of the body, and the coronary vessels, which feed the heart. Whendeposits accumulate in localized regions of a blood vessel, stenosis, ornarrowing of the vascular channel, occurs. Blood flow is restricted andthe person's health is at serious risk.

[0006] Numerous approaches for reducing and removing such vasculardeposits are known, including balloon angioplasty, in which aballoon-tipped catheter is used to dilate a region of atheroma;atherectomy, in which a blade or cutting bit is used to sever and removethe atheroma; spark gap reduction, in which an electrical spark burnsthrough the plaque; and laser angioplasty, in which laser energy is usedto ablate at least a portion of the atheroma. In order to facilitatetreatment of the stenosis, it is often desirable to obtain a visualimage of the interior of the blood vessel within the region of interest.Catheters having imaging elements such as ultrasonic transducers areoften used to obtain these images.

[0007] In many cases, catheter systems having imaging or interventionaldevices will include a rotatable drive cable disposed within theflexible catheter body. Catheters of this type will have some type ofwork element fixed to the distal end of the drive cable. In imagingsystems, the work element is typically an ultrasonic transducer or amovable mirror associated with an ultrasonic transducer.

[0008] An exemplary catheter system having a rotating ultrasonictransducer coupled to a drive cable is disclosed in U.S. Pat. No.4,794,931, the disclosure of which is incorporated herein by reference.In this system, a drive cable disposed within a flexible tubularcatheter body is used to rotate an ultrasonic transducer about an axisparallel to the catheter body. The ultrasonic transducer is therebycaused to scan a region of the blood vessel in a plane normal to thecatheter body.

[0009] In yet another exemplary catheter system of particular importanceto the present invention, a catheter body is provided with a guidewireengagement sheath design, where the catheter is introduced over aseparate (moveable) guidewire. A catheter system of this type isdisclosed in U.S. Pat. No. 5,203,338, which is fully incorporated hereinby reference. In this particular catheter system, the catheter body hasa guidewire lumen attached at the distal end of the catheter body. Theguidewire lumen and the primary lumen are separated by a wedge, whichensures that the drive cable does not proceed beyond the primary lumenand into the guidewire lumen.

[0010] A catheter of the type having a guidewire engagement is used asfollows. A guidewire is advanced into the patient until it lies within aregion of interest, typically a region of stenosis within the bloodvessel. After the guidewire is positioned, the proximal end of theguidewire is fed into the guidewire lumen of the catheter. The catheteris then advanced into the patient over the guidewire. Advancement of thecatheter into the patient continues until the primary lumen distalregion lies within the blood vessel in the region of interest. Asuitable work element, such as a rotatable imaging core, may bedelivered while positioned in the primary lumen.

[0011] A general concern in the development of each type of cathetersystem described above, and in catheter system development in general,is the ability to achieve consistency in reliability and performanceamong catheters employing a particular system. In response to thisconcern, approaches have been identified which may provide techniquesfor improving common components of these catheter systems to provideconsistent reliability and performance.

[0012] One such approach of particular interest to the presentinvention, includes improvement of the hub assembly. The hub assemblyprovides, among other things, electrical coupling to the rotatingtransducer or other work element. Rotation of the transducer elementmakes it necessary to transmit an electrical signal through a fixedferrite wire to a transducer lead wire disposed within the rotatingdrive cable. The signal is transmitted between the fixed and rotatingwires through the well-known electrical process of induction. Generally,this process includes using two ferrites separated by a small air gap,where the first ferrite rotates relative to a second fixed ferrite. Thefirst ferrite, when charged, produces an electromagnetic field. Thesecond ferrite, in close proximity to the first ferrite and itselectromagnetic field, causes the introduction of inductance into thecircuit. The gap is generally necessary to remove the negative effectsof friction which occur whenever a rotating body contacts a fixed body.However, as in most rotary transformers, there are losses of power andother inefficiencies inherent in this transmission. For example, it isgenerally difficult without labor intensive and expensive manufacturingprocesses, to provide a consistent gap size. Without a consistent gap,the output performance of the transformer can vary between hubassemblies. Moreover, it can be difficult to ensure that the rotatingferrite rotates with enough precision to avoid inadvertently contactingthe fixed ferrite.

[0013] A number of other approaches for improving catheter systems aredirected at the drive cable. The drive cable is coupled via a driveshaft to a drive motor. The drive cable runs substantially the length ofthe catheter body, and serves as a flexible, torque-transmitting elementto rotate the electrical transducer. The drive cable is constructed withcoils in order to provide torsional stiffness and flexibility. Thisenables the drive cable to traverse the tortuous lumen of the humanvascular system. A drive cable, which may include transducer lead wiressurrounded in a coaxial fashion by a coiled cable body, is disclosed inU.S. Pat. No. 5,503,155, the disclosure of which is incorporated hereinby reference.

[0014] One potential drawback to the drive cable described above is itssusceptibility to stretching. Stretching of the drive cable is typicallyencountered during removal procedures, during pullback sequences, wherethe imaging core is retracted within the flexible catheter body toobtain longitudinal imaging sequences, or else during flushingoperations. Upon removing the catheter from the intravascular lumen, theuser must “pull back” on the proximal end of the catheter body.Generally, movement of the catheter can be restricted when the catheterbody encounters friction between the catheter body and the walls of theintravascular lumen. When movement of the catheter body is restricted inthis manner, the coils of the drive cable can stretch in a mannersimilar to coils of a spring. The coils can also be stretched apart whenthe catheter body is being flushed-out with a flushing fluid. In thiscase, the flushing fluid creates a piston effect on the coils and workelement, thus spreading the coils apart.

[0015] While a stretchable drive cable may be advantageous for somepurposes, it can also be problematic. Transducer lead wires, disposedand anchored within the drive cable lumen, do not have the ability tostretch and when subjected to tensile forces, the transducer lead wirestend to break which creates a break in the electrical continuity of thesystem.

[0016] Other improvements to catheter systems may include re-directingflushing fluids from exiting through a side port positioned at thedistal end of the primary lumen. Generally, the side exit port workswell, however, the side exit port can be a nuisance in a clinicalsetting since it is difficult to know which way the side exit port ispointing during flushing procedures.

[0017] For these reasons, it would be desirable to provide an improvedcatheter system for use with internal work elements, such as ultrasonicimaging transducers. It would be particularly desirable to provide acatheter system that has an improved hub assembly that permits efficientelectrical induction to provide a more consistent and reliable signal tothe transducer element. It would be further desirable if the drive cableof the catheter were configured to prevent the internal electricaltransmission line from breaking should the drive capable be forced tostretch, such as when the user is pulling back or flushing the catheterbody. It would be still further desirable if the catheter body wereformed with a primary lumen and a guidewire lumen that would provide adistal exit port for the egress of flushing fluids parallel to thedirection of blood flow. At least some of these objectives and more aremet by the invention described hereinafter.

SUMMARY OF THE INVENTION

[0018] The present invention is directed to an improved catheter systemhaving a work element coupled to a drive cable disposed within a lumenof a flexible tubular catheter body. The work element generally includesan ultrasonic imaging transducer. One advantageous improvement describedin more detail below, includes a reconfiguration of ferrites in the hubassembly, such that a gap, typical between the ferrites, is reduced oreliminated. In reducing or eliminating the gap it is meant that theaverage clearance between two facing surfaces of the ferrites will beless than 0.0005 in., preferably less than 0.0002 in., and mostpreferably less than 0.0001 in. In reducing or eliminating the gapclearance in this manner, manufacture of the hub assembly can be donewith less precision, which makes the overall fabrication process simplerand less expensive. Moreover, by reducing or eliminating the gapclearance, the inductive transmission of the electrical signal can beaccomplished with more efficiency and with reduced transmission losses.

[0019] Another improvement lessens the potential for tensile failure ofthe electrical transmission lines when subjected to stretching. In oneembodiment, a strain relief member is provided proximate and parallel tothe transmission lines. The transmission lines are arranged slackedrelative to the strain relief member. Thus, when the transmission linesand strain relief member are subjected to stretching forces, usuallycaused by either flushing and/or pull-back operations, the strain reliefmember and not the transmission lines is subjected to the forces.Accordingly, the transmission lines are protected. In an alternativeembodiment, a portion of the transmission lines is looped in a mannersimilar to the coils of a spring. In this configuration, the lines canextend when subjected to a pulling force and retract when the force isremoved.

[0020] Another improvement to the catheter system includes a drive cablefabricated as a multi-layered structure where each layer includes acounter-wound coil. The coils may either expand or contract as the drivecable rotates which increases the interference between the multiplelayers and thus increases the torque transmission capability of thedrive cable. At the same time, the multi-layered coil structure allowsthe drive cable to maintain the requisite flexibility.

[0021] In yet another improvement, the distal tip of the catheter bodyhas a lumen positioned between the catheter lumen and the guidewirelumen to allow flushing fluid or other fluids to be released through adistal port of the guidewire lumen.

[0022] Another improvement to the catheter system may include cathetertubing having multiple tubing portions of varying material strengths,stiffnesses, and/or wall thicknesses. For example, a tubing portion maybe provided having an intermediate tubing stiffness relative to a stiffproximal portion of the catheter body and a highly flexible distalportion. The intermediate portion may be placed between the proximal anddistal portions to provide a transitional area. The transitional areaincreases the practitioner's ability to advance the catheter into a bodylumen without kinking or bending the catheter body.

[0023] Another improvement may include increasing the imaging region inthe distal tip without increasing the length of the distal tip. Thedrive cable with the imaging device is moved forward into a space in thedistal portion created by removing some internal portion or portions ofthe distal portion of the primary lumen. Thus, the imaging plane canpenetrate deeper into the vasculature, effectively moving the imagingplane distally.

[0024] In one aspect of the present invention, an improved cathetersystem of the type including (a) a tubular catheter body having aproximal portion, a distal portion, and a lumen therethrough; and (b) adrive cable rotatably received in the lumen, is provided. The improvedcatheter system includes a hub assembly secured to a proximal end of thedrive cable. The hub assembly includes a rotary transformer, which has afirst ferrite core and a second ferrite core. The second ferrite corecontacts the first ferrite core with substantially zero clearancetherebetween, as defined above, to promote electrical induction betweeneach core.

[0025] In another aspect, an improved catheter system of the typeincluding (a) a tubular catheter body having a proximal portion, adistal portion, and a primary lumen therethrough; and (b) a drive cablehaving a cable body and a cable lumen rotatably received in the lumen,where the drive cable has at least one lead wire disposed in the cablelumen. The improvement includes a support member disposed proximate tothe lead wire to provide strain relief to the lead wire when the leadwire is subjected to a tensile force. The support member can withstandlarger tensile forces than the lead wires. Usually, the support membercan withstand at least about 100% to 200% more tension than the leadwires, preferably at least about 300%. The support member extendssubstantially the entire length of the lead wire, usually about 75% to85% of the length, preferably about 95% to 100%.

[0026] In yet another aspect, an improved catheter system of the typeincluding (a) a tubular catheter body having a proximal portion, adistal portion, and a primary lumen therethrough; and (b) a drive cablehaving a cable body and a cable lumen rotatably received in the primarylumen, where the drive cable has at least one lead wire disposed in thecable lumen, is provided. The improvement includes a strain reliefdevice coupled to a portion of the drive cable. The strain relief devicecauses the lead wires to be biased, typically with a spring or similardevice, such that the lead wires can extend or retract from within thedrive cable. The movement of the lead wires keeps the lead wire frombeing directly subjected to tensile forces which may cause the leadwires to break.

[0027] In yet another aspect, an improved catheter system of the typeincluding (a) a tubular catheter body having a proximal tubular portion,a distal tubular portion, and a lumen therethrough, and (b) a drivecable rotatably received in the lumen, is provided. The improvementincludes an intermediate tubular portion formed on the tubular catheterbody from a transitional material. The intermediate portion can beplaced between two portions on the tubular catheter body having similaror dissimilar flexural stiffnesses and/or strengths. Preferably, thetransitional material has a greater flexural stiffness than the distaltubular portion and a lower flexural stiffness than the proximal tubularportion. Generally, the intermediate portion can have a flexuralstiffness of between 50 kpsi and 200 kpsi, preferably between about 150kpsi and 190 kpsi.

[0028] In yet another aspect, an improved catheter system is provided ofthe type including (a) a tubular catheter body having a proximalportion, a distal portion, and a primary lumen therethrough, (b) aguidewire lumen coupled coaxially with the primary lumen on the distalportion of the catheter with a wedge in between each lumen; and (c) adrive cable rotatably received in the primary lumen. The improvementincludes a wedge lumen formed in the wedge to allow communicationbetween the primary lumen and the guidewire lumen. The wedge lumen ispreferably smaller in diameter than the primary lumen. The wedge lumenis preferably between about 0.01 in. and 0.3 in. in diameter, preferablybetween about 0.012 in. and 0.1 in.

[0029] In yet another aspect, an improved catheter system is provided ofthe type including a tubular catheter body having a proximal portion, adistal portion, and a lumen therebetween, where the lumen is capable ofrotatably receiving a drive cable therethrough. The improvement includesa drive cable which has an inner coil and an outer coil. The coils beingwound in opposing directions so that the inner coil expands when thedrive cable is rotated and where the outer coil contracts when the drivecable is rotated.

[0030] In yet another embodiment, an improved catheter system isprovided of the type including a tubular catheter body having a proximalportion, a distal portion, and a lumen therethrough. The improvementcomprises a first tubular member and a second tubular member arranged ina telescoping engagement, where the first tubular member is formed atleast in part from a material, comprising a plastic or a polymermaterial, such as polyetheretherketone (PEEK).

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 illustrates an exemplary embodiment of a vascular catheteraccording to the present invention.

[0032] FIGS. 2A-2D illustrate the catheter of FIG. 1, having a hub, aproximal portion, further comprising a proximal tube and a distal tube,mating connectors, drive cable, and a distal portion of the catheterbody.

[0033]FIG. 3 illustrates the drive cable having a drive cable body, acarrier, and an ultrasonic imaging transducer.

[0034]FIG. 4 is a cut-away view of the drive cable body of FIG. 3.

[0035]FIG. 4A illustrates a cross-sectional view of the drive cable ofFIG. 3.

[0036]FIG. 5 illustrates an alternative embodiment of drive cable coilsaccording to the present invention.

[0037]FIG. 6 illustrates a strain relief device according to aspects ofthe present invention.

[0038]FIG. 7A is a cross-sectional view of the hub assembly having arotary transformer according to principles of the present invention.

[0039]FIG. 7B is a cross-sectional view of the hub assembly of FIG. 7.

[0040]FIG. 8 illustrates a portion of the distal end of the catheterbody showing the primary lumen, the guidewire lumen, and the wedge lumenconstructed in accordance with the principles of the present invention.

[0041]FIG. 9 illustrates the distal end of the catheter body with ashortened distal tip.

[0042]FIG. 10 illustrates an intermediate strength sheath portiondisposed between the proximal and distal sheath portions according toprinciples of the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0043] A vascular catheter system is provided having a catheter bodywith a proximal portion and a distal portion, both having a proximalend, a distal end and a primary lumen therebetween. This distal portionfurther includes a guidewire lumen preferably disposed coaxial with, anddistal to the primary lumen. A drive cable is disposed within theprimary lumen, which is usually axially translatable within the lumenand rotatable about its own longitudinal axis. The drive cable carries awork element at its distal end, typically being an ultrasonic imagingtransducer, but optionally being an interventional device. The outerdiameter of the drive cable may be varied to accommodate variations insize of the catheter body.

[0044] Provided at the proximal end of the drive cable is a tuning hubassembly. The hub assembly, among other things, provides the ability tomatch the impedance between a transmitter/receiver and the work element.In some cases, the work element may be an ultrasonic transducer, whichmay have a variable center frequency output. For example, a transducerused in very small coronary vessels may require a higher frequencyoutput (about 30 MHz and above), while transducers for use in a largevessel, such as the aorta, may require a lower frequency output (about30 MHz and below). The variable frequency requirement createsvariability in the electrical load perceived by the electronic circuitryof the transmitter/receiver. Most transmitters/receivers work mostefficiently when subjected to a consistent load. Therefore, theimpedance between the transducer and the transmitter/receiver arematched, using an impedance matching circuit, which can account for thevariableness in the transducer frequency. To ensure consistency ofperformance and fabrication in the impedance matching circuit, thecircuit may be fabricated on a circuit board. The circuit board can beplaced in the most economic and efficient position in the hub housing.Preferably, the circuit board is positioned toward the proximal end ofthe hub housing. Moreover, by placing the circuit on a circuit board,the circuit can be designed and tested prior to fabrication of the hubassembly. Furthermore, should the circuit fail for any reason, thecircuit board can be easily replaced.

[0045] Referring now to FIGS. 1 and 2, an improved vascular cathetersystem 10, according to the principles of the present invention, isillustrated. The improved vascular catheter system 10 includes acatheter body 12 having a reduced profile distal portion. Catheter body12 include a proximal portion 14 and a distal portion 16, each having aproximal end, a distal end, and a primary lumen 18 therebetween. Thedistal portion 16 will extend from the distal end of the catheter bodyto an adhesive or other joint 20 to, and including a female luer fitting22. The proximal portion 14 will extend from the proximal hub assembly24 to a second adhesion or other joint 26 to and including the male luerfitting 28. The proximal portion will have a single primary lumen 18extending through it and a reduced cross-sectional distal area tofacilitate entry into coronary blood vessels and/or tight stenoticlesions.

[0046] Proximal portion 14 will have a somewhat larger cross-sectionalarea to accommodate a distal tube 30 and a proximal tube 32 joinedtogether in a telescopic engagement. Proximal telescoping tube 32 ismoveable in and out in a coaxial fashion, into distal telescoping tube30. By telescoping these two members with respect to one another, theoperator may change the effective length of the catheter body. Theeffective length change can result in an increased, axial translation bythe drive cable 34 of work element 36.

[0047] Preferably, proximal telescoping tube 32 and distal telescopingtube 30, are made of a polymer or plastic material, which providesadequate bending stiffness and resistance to substantially large hoopstresses. In one alternative embodiment, proximal tube 32 may be allmetallic. Accordingly, telescoping tubes 30 and 32 can be prevented frombending or kinking, during pull-back or other operations. Thus, byincreasing the stiffness of the tubes, the catheter system avoids atleast some of the effects of Non-Uniform Rotational Distortion (NURD).Furthermore, a stiff male telescoping tube 32 can provide easiermanipulation of the telescope, allowing a practitioner one push,full-stroke capability. The single stroke capability provides a clearerimaging sequence, since incremental advancing of tube 32 is eliminated.Also, the male tube 32 outside diameter can be reduced, which allows forreduction of the female tube 30 outside diameter, as well. Moreover,distal tube 30 having a relatively high bending stiffness, eliminatesthe need for using embedded braiding of the tube or stiffeningmechanisms, such as Nitinol® or stainless steel stiffening mandrels.

[0048] To provide the requisite strength, preferably, catheter body 12and telescoping tubes 30 and 32 can be made of a wide variety ofbio-compatible materials, typically made from natural or syntheticpolymer or plastic materials or Nitinol® or similar alloys and othermetals. These materials may include silicone rubber, natural rubber,polyvinylchloride, polyurethanes, polyesters, polyethylene,polytetrafluoroethylene (PTFE), and the like, but preferablypolyetheretherketone (PEEK).

[0049] The mating connector assembly 40 includes a first connector ormale luer fitting 28 secured to the distal end of the proximal portion14 and a second connector or female luer fitting 22 secured to theproximal end of the distal portion 16. The connectors may be selectivelyconnected to each other to join the lumens of the proximal and distalportions together in a continuous, axially fixed relationship. Matingfemale and male luer fittings 22,.28 are adhesively attached or moldedto the proximal and distal portions of the catheter body, respectively.In a preferred embodiment, male luer fitting 28 may be adhesivelyattached 26 to the distal end of the telescope assembly 42. Female luerfitting 22 may be insert molded or similarly coupled to the proximal endof the proximal catheter body. Mating connector assembly 40 will allowthe user, who is having difficulty crossing a lesion, the option toexchange a distal sheath with a short guidewire lumen, for a sheathhaving a longer distal portion. The user will also be capable ofreplacing failed parts attached to either the proximal or distalportions 14, 16 without having to discard the entire catheter system.

[0050] In a preferred embodiment, male luer fitting 28 may have anextended portion 44 at adhesive point 26. The extended portion allowsmore room in the catheter system for making additional positioningadjustments to the drive cable and work element to ensure that the workelement is placed at the correct location during assembly. The femaleluer fitting having the extended portion is commercially available fromB. Braun Medical Inc. of Bethlehem, PA and other known vendors.

[0051] Referring now to FIGS. 3-5, another embodiment of the cathetersystem 10, constructed in accordance with the principles of the presentinvention, are described. Drive cable 34 is preferably an elongatetubular or cylindrical member having a generally circular cross-sectionwith a sufficient torsional rigidity to transmit torque from theproximal end to the distal end of catheter body 12. In an exemplaryembodiment, drive cable 34 includes drive cable body 60 which has aflexible, counter-wound coil 62 including an outer coil 64 and innercoil 66. An electrical transmission line 72 is received within a lumen70 of drive cable body 60.

[0052] Drive cable 34 is flexible so that it may be introduced within acatheter or sheath through tortuous body passages, such as the coronaryarteries, to a target location of interest. Drive cable 34, preferablyhas a bending stiffness constant in the range from 0.015 to 0.15in-lb-in, preferably from 0.025 to 0.050 in-lb-in. Drive cable 34incorporates an ultrasonic transducer 56 at its distal end and acoupling element 57 at its proximal end. The outer diameter of drivecable body 60 may be varied to accommodate variations in the size of thecatheter body 12. For example, in one embodiment, the outer diameter ofthe drive cable 34 may be reduced from 0.029″to 0.022″so that thecatheter body 12 can also be reduced in diameter. A benefit of such areduction in size is improved catheter preparation (specificallyflushing), due to the increased clearance between the drive cable 34 andthe catheter body 12.

[0053] According to the present invention, the pair of nested,counter-wound helical coils, 64 and 66 are each formed from metal wire,such as 304V stainless steel or the like. Each coil in the cable iswound in opposite directions so that when the cable body is rotated, oneof the coils will tend to tighten (usually outer coil 64), while theother coil expands (usually inner coil 66). This provides the cable witha very high torsional modulus of elasticity, while reducing the flexuralmodulus of elasticity, due to the flexible nature of the coilstructures. In one embodiment, inner coil 66 will have a diameter in therange from about 0.017 to 0.019 inches, while outer coil 64 will have adiameter in the range from about 0.029 to 0.031 inches. The wirediameter of the coils will usually be in the range from about 0.002 to0.004 inches, more usually being in the range from 0.0025 to 0.0035inches.

[0054] In an alternative embodiment, more than two coils may be used inthe counter-wound drive cable, so long as the additional coils do notincrease the overall diameter of drive cable body 60 or decrease thediameter of the drive cable lumen 70, beyond the desired range.Preferably, as shown in FIG. 5, three coils can be used. In thispreferred example, outer coil 64 is wound clockwise. Inner coils 66 and66′ are wound counter-clockwise. When drive cable 34 is rotatedclockwise, outer coil 64 contracts and inner coils 66 and 66′ expand.This configuration provides a very high torsional modulus of elasticity,while maintaining a reduced flexural modulus of elasticity. Optionally,it may be desirable to cover outer coil 64 with an elastomeric sheath inorder to enhance mechanical integrity of the coil and facilitaterotation of the cable body with any catheter lumen or sheath. Suitableelastomeric sheath materials include polyurethane, silicone, and thelike, preferably polyester.

[0055] Referring now to FIGS. 4 and 4A, as previously mentioned,electrical signal connection between the distal end and the proximal endof cable body 60 will typically be provided by an electricaltransmission line 72 extending through cable body lumen 70. Lines 72 maybe formed from an electrically conductive metal, such as silver, platedcopper, copper, silver, gold, aluminum, and various alloys thereof. Themetal core wires may be covered by a conventional insulating material,such an organic polymer, such as polyurethane, polyester, nylon, and thelike. Typically, the overall diameter of the wires may be in the rangeof 0.005 to 0.050 inches, usually from 0.005 to 0.030 inches. In oneexemplary embodiment, electrical transmission lines 72 may be in theform of a coaxial transmission line, however, line 72 need not be in acoaxial line configuration, but instead can be oriented in an axiallyparallel manner, twisted pair, or could be irregularly wound over oneanother without departing from the intent of the present invention.

[0056] In operation, when primary lumen 18 is being flushed or when thecatheter body is being pulled-back, drive cable 34 can be stretched.When stretched, counter-wound coils 62 perform similar to a spring andtend to elongate. As shown in FIG. 4 and 4A, electrical transmissionlines 72 are disposed within the axial lumen 70 of cable body 60 with astrain relief member 68. Strain relief member 68 has a higher tensilestrength than electrical transmission lines 72. Although drive cable 34is mechanically suited for stretching, strain relief member 68 will tendto absorb the tensile load induced and relieve electrical transmissionlines 72 -from the tensile forces, which would otherwise be completelyapplied to the weaker electrical transmission lines 72.

[0057] In an alternative embodiment, strain relief may be provided tolead wires 72 by a service loop device 80, as shown in FIG. 6.Preferably, service loop device 80 is coupled to rotary shaft 82,disposed in hub assembly 24. In operation, internal lead wire 84 isdisposed within device 80 in a looped configuration 86. Loop 86 biaseswire 84, such then when cable 34 is stretched, loop 86 contractsallowing lead wire 84 to move axially, within the stretching cable.Advantageously, when drive cable 34 is no longer being stretched, wireloop 84 returns to its original looped configuration 86. Loop device 80will provide an enclosed chamber 87, which protects hub assembly 24 frombeing subjected to body or flushing fluids that would otherwise beallowed to enter wire access port 85.

[0058] Referring now to FIG. 7A, another embodiment of a catheter system10, constructed in accordance with the principles of the presentinvention, is described. Hub assembly 24 includes a hub housing 90, arotary transformer 92, and a circuit board 94, among other things.

[0059] In one exemplary embodiment, rotary transformer 92 includes twoferrites 96 and 98. Ferrites 96 and 98 are provided for creating aninductive current, which transfers an electrical signal from circuitboard 94, through rotating transducer leads 72, to transducer 36.

[0060] As can be appreciated from FIG. 7A, fixed ferrite wire 100 bringsthe electrical signal from circuit board 94 to ferrite 98. Ferrite wire100 is fed through a hole formed through ferrite 98, turned a number oftimes around ferrite 98 to create a first set of ferrite windings, andfed back out the hole. Similarly, a hole is formed through ferrite 96,such that electrical transmission line 72 can be fed through the hole,wound a number of times about the inside of the ferrite to create asecond set of ferrite windings, and finally fed back out through thehole.

[0061] Rotary transformer assembly 92 is rotatably disposed in a hubhousing, such that the first and second set of windings are aligned witheach other to form inductive coupling. An electrical current flowingwithin ferrite wire 100 will pass through the first set of ferritewindings, which creates a magnetic field around ferrite 98. The secondset of windings on rotating ferrite 96 are within this magnetic field,which induces a corresponding electrical current flow through electricaltransmission line 72. The reverse will also be true - a current flowingthrough the electrical transmission line will induce a current withinferrite wire 100.

[0062] As shown in FIG. 7B, ferrites 96 and 98 contact each other atpoint 106. The clearance at point 106 is substantially zero. Normally,zero clearance is problematic when one ferrite rotates relative to theother ferrite. However, rotary transformer 92, in this application, isnot expected to perform for a long period of time, preferably less than60 minutes. Moreover, hub assembly 24 is disposable. Thus, negativeeffects due to friction at point 106 can be deemed negligible.Optionally, to reduce friction at point 106, a Mylar®, or similarmaterial, may be disposed between ferrites 96 and 98.

[0063] In the above example, ferrite 96, rotates with rotary drive shaft82. In an alternative embodiment, ferrite 98 may rotate, while ferrite96 is fixed.

[0064] In another alternative embodiment, a biasing member 108 ispositioned between hub housing 90 and the fixed ferrite to bias thefixed ferrite against the rotating ferrite. The stationary ferrite doesnot rotate, but it is free floating. The biased, fixed free floatingferrite is pressed against the rotating ferrite to ensure that there isno air gap between them. Moreover, biasing member 108 and the freefloating ferrite removes the need for precision fabrication of rotarytransformer assembly 92. For example, if rotating ferrite is impreciselypositioned on the rotary drive shaft it may begin to wobble whenrotated. Biasing member 108 will press the fixed, free floating ferriteagainst the wobbling rotating ferrite. Since the stationary ferrite isfree floating it will tend to wobble in sync with the rotating ferrite,thus preserving contact between the ferrites.

[0065] Referring now to FIG. 8, another embodiment of catheter body 10,constructed in accordance with the principles of the present invention,is described. One embodiment of catheter system 10 includes a catheterbody 12 having a primary lumen 150 and a guidewire lumen 152. Thecatheter body is formed by inserting a length of polymeric material intothe distal end of primary lumen 150. Shaped mandrels are used to formwedge 154 so that it has a distal inclined surface 156 and a proximalinclined surface 158. Wedge 154 can be formed from any organic polymerhaving the requisite mechanical properties as well as processability.Distal inclined surface 156 may be formed as part of guidewire lumen 152which extends from guidewire exit port 160 to distal port 162, so thatit may receive a guidewire. Alternatively, the wedge could comprise aspring coil.

[0066] Tapered wedge 154 has a wedge lumen 164 which providescommunication between primary lumen 150 and guidewire lumen 152. Wedgelumen 164 allows fluid to exit primary lumen 150 into guidewire lumen152, for removal of flushing fluids through distal port 162 of thecatheter body. Wedge lumen 164 will have a diameter of between about0.003 to 0.025, preferably about 0.011. In any event, wedge lumen 164diameter is smaller than the diameter of distal housing 166 to preventthe working element 168 from mininizing flow through wedge lumen 164.

[0067] Referring now to FIG. 9, another embodiment of catheter system10, constructed in accordance with the principles of the presentinvention, is described. As described above, catheter body 12 isadvanced over a guidewire until the distal end portion reaches or lieswithin the region of interest 200. Work element 202 is moved withrespect to catheter body 12 until work element 202 is in the properposition to perform the diagnostic function. As can be appreciated fromFIG. 9, when working element 202 is in position, the distal tip 204 ofthe catheter body may extend beyond stenotic site 200, a length Y.Length Y may become problematic if, for example, as shown in the figure,the anatomy of the vasculature 206 does not permit the distal tip toextend far enough beyond the area to be imaged 200. To resolve thisproblem, length Y of distal tip 204 may be made shorter. Generally,length Y can be reduced between about 90% and 30%. In one example,length Y is reduced from about 3 cm to 1.5 cm.

[0068] In order to shorten length Y, while maintaining column strengthin guidewire lumen 210 to support the guidewire, the outside diameter Dof tip 204 may be made larger. Outside diameter D can be increased up toabout 2 mm, preferably about 1 mm. Alternatively, space may be added inprimary lumen 150 by removing the proximal inclined surface 212 of wedge214. Removing the incline from surface 212 allows working element 202 tobe pushed farther forward toward surface 212, which can compensate forthe shorter length Y.

[0069] Referring now to FIG. 10, another embodiment of catheter system10, constructed in accordance with the principles of the presentinvention, is described. As described above, the proximal section ofcatheter body 12 generally has a relatively high bending stiffness toprovide pushability to the catheter. By contrast, the distal tip ofcatheter body 12 is made highly flexible to easily navigate the tortuouslumen of the vasculature. Typically, when catheter body 12 is deliveredinto a patient, frictional or other impeding forces may resist theentry, especially from a hemostasis valve. As a practitioner continuesto push the catheter body forward in spite of the resistance, theportion of the flexible distal sheath remaining outside of the patientduring the introduction process, may tend to bend or kink.

[0070] In this embodiment, a transition or intermediate catheter sheathportion 217 is formed into catheter body 12. Intermediate sheath portion217 can be adhesively, thermally, or similarly bonded between a proximalsheath portion 216, at point 222, and a distal sheath portion 218, atpoint 220. The portions can also be connected using a lap joint, buttjoint, or the like. Intermediate sheath portion 217 provides a smoothtransition between the relatively stiff proximal sheath portion 216 andthe flexible distal tip 218. Transition portion 217 adds a level ofgradually increasing stiffness or column strength, to overcomefrictional and other forces, to allow easier advancing of the catheterbody 12 into the vasculature of the patient. In one embodiment,intermediate sheath portion 217 can be between about 20 to 200 mm long,preferably 40 to 100 mm. Intermediate sheath portion 217 will begin atpoint 220, which is between about 100 to 400 mm from distal tip 204 ofcatheter body 12, preferably 150 mm. Intermediate portion 217 willtransition into proximal sheath section 216 at approximately point 222.

[0071] As previously described, proximal sheath portion 216 can be madefrom a variety of polymers, including preferably PEEK. Distal sheathportion 218 is typically made from a highly flexible polyethylene orsimilarly flexible material. Intermediate sheath portion 216 can be madefrom materials that have a stiffness ranging between that of sheathportions 216 and 218. Commonly, the flexural modulus of portion 217 canrange from 50 to 220 kpsi, preferably ranging between 150 to 190 kpsi.These materials include nylons, polyesters, polyimides, and polyolefins,including blends of these materials.

[0072] Although the foregoing invention has been described in detail forpurposes of clarity of understanding, certain modifications may beobvious to those skilled in the art. Thus, the scope of the inventionshould be construed with reference to the appended claims including thefull range of equivalents to which the inventor is entitled.

What is claimed is:
 1. An improved catheter system of the type including(a) a tubular catheter body having a proximal portion, a distal portion,and a lumen therethrough; (b) a drive cable rotatably received in thelumen; and (c) a hub assembly secured to a proximal end of the drivecable, wherein the improvement comprises a rotary transformer disposedwithin the hub assembly, the rotary transformer including a firstferrite core and a second ferrite core, the second ferrite corecontacting the first ferrite core with substantially zero clearancetherebetween to promote electrical induction between each core.
 2. Theimproved catheter system of claim 1 wherein the first ferrite core isstationary, and wherein the second ferrite core is rotatable.
 3. Theimproved catheter system of claim 2, wherein the rotary transformerfurther comprises a friction limiting material disposed between therotating ferrite core and the fixed ferrite core.
 4. The improvedcatheter system of claim 1, wherein the first ferrite core is biasedagainst the second ferrite core.
 5. The improved catheter system ofclaim 1, wherein the first ferrite core is free floating within the hubassembly.
 6. An improved catheter system of the type including (a) atubular catheter body having a proximal portion, a distal portion, and aprimary lumen therethrough; and (b) a drive cable having a cable bodyand a cable lumen rotatably received in the lumen, having at least onelead wire disposed in the cable lumen, wherein the improvement comprisesa support member disposed within the cable lumen to provide strainrelief to the lead wire when the lead wire is subjected to a tensileload, the support member extending substantially the entire length ofthe lead wire.
 7. The improved catheter system of claim 6, wherein thesupport member comprises a flexible multi-filament material.
 8. Theimproved catheter system of claim 6, wherein the support membercomprises Kevlar®.
 9. The improved catheter system of claim 6, whereinthe support member comprises a liquid crystal polymer.
 10. An improvedcatheter system of the type including (a) a tubular catheter body havinga proximal portion, a distal portion, and a primary lumen therethrough;and (b) a drive cable having a cable body and a cable lumen rotatablyreceived in the primary lumen, having at least one lead wire disposed inthe cable lumen, wherein the improvement comprises a strain reliefdevice coupled to a portion of the drive cable, the strain relief deviceallowing the lead wire to move within the cable lumen when placed intension.
 11. An improved catheter system of the type including (a) atubular catheter body having a proximal tubular portion, a distaltubular portion, and a lumen therethrough, and (b) a drive cablerotatably received in the lumen, wherein the improvement comprises anintermediate tubular portion formed on the tubular catheter body of atransitional material between the proximal tubular portion and thedistal tubular portion, the transitional material being of a higherflexural modulus than the distal tubular portion and of a lower flexuralmodulus than the proximal tubular portion.
 12. The improved cathetersystem of claim 11, wherein the proximal tubular portion comprises amaterial taken from the group consisting of a natural or syntheticpolymer or plastic material, such as silicone rubber, natural rubber,polyvinylchloride, polyurethanes, polyesters, polyethylene,polytetrafluoroethylene (PTFE), and polyetheretherketone (PEEK).
 13. Theimproved catheter system of claim 11, wherein the intermediate tubularportion comprises a material taken from the group consisting of nylons,polyester, polyimides, polyolefins, and blends of such materials.
 14. Animproved catheter system of the type including (a) a tubular catheterbody having a proximal portion, a distal portion, and a primary lumentherethrough, (b) a guidewire lumen coupled coaxially with the primarylumen on the distal portion of the catheter, having a wedge in betweensaid lumens; and (c) a drive cable rotatably received in the primarylumen, wherein the improvement comprises a wedge lumen formed in thewedge allowing communication between the primary lumen and the guidewirelumen.
 15. An improved catheter system of the type including (a) atubular catheter body having a proximal portion, a distal portion, and alumen therethrough, and(b) a drive cable rotatably received in thelumen, wherein the improvement comprises the drive cable comprising afirst inner coil, a second inner coil, and an outer coil, the outer coilbeing wound in a direction opposite to the inner coils, the first innercoil expanding against the outer coil and the second inner coilexpanding against the first inner coil when the drive cable is rotated,thereby increasing the column strength of the drive cable.
 16. Theimproved catheter system as in claim 15, wherein the outer coilcontracts against the first inner coil when the drive cable is rotated.17. An improved catheter system of the type including (a) a tubularcatheter body having a proximal portion, a distal portion, and a lumentherethrough, and (b) a drive cable rotatably received in the lumen,wherein the improvement comprises a first tubular member and a secondtubular member arranged in a telescoping engagement, wherein the firsttubular member is formed at least in part from a material, the materialbeing a plastic or a polymer material, such as polyetheretherketone(PEEK).